1. Field of the Invention
The present invention relates generally to an antenna, and more particularly to a multi-frequency antenna for mobile device.
2. Description of Prior Art
With fast development of wireless communication, an antenna plays more and more important role thereof. In order to be installed inside an electronic device, the antenna needs lower profile, comprehensive functional, etc.
As it is known to all, a kind of antenna called PIPA has been widely used in mobile device. And even a double-frequency PIFA also utilized in wireless communication. The double-frequency PIFA includes a first radiating arm, a second radiating arm, a short circuit arm, a grounding portion and a feeding line. The first radiating arm and the second radiating arm are connected to one end of the shirt circuit arm and extend along opposite direction. The other end of the shirt circuit arm is coupled to the grounding portion. The feeding line is connected to a feeding point on the shirt circuit arm. Thus, the antenna may works at two frequencies.
However, the double-frequency antenna is relatively larger and takes up more space inside of the mobile device. In addition, once the antenna is completed, and the frequency is invariable.